optimize alarm

[lpcy]

Fix alarm webhook server frequently receives empty messages

• Add a unit test to verify that the fix works.
• The alarm core does not judge whether the filteredmessages is empty before sending.

• If this pull request closes/resolves/fixes an existing issue, replace the issue number. Closes #.
• Update the CHANGES log.

[wu-sheng]

Seems harmless.

[codecov]

Codecov Report

Merging #6816 (96a38e4) into master (1ecbb50) will decrease coverage by 30.31%.
The diff coverage is 10.00%.

❗ Current head 96a38e4 differs from pull request most recent head fe80ab2. Consider uploading reports for the commit fe80ab2 to get more accurate results

@@              Coverage Diff              @@
##             master    #6816       +/-   ##
=============================================
- Coverage     58.76%   28.44%   -30.32%     
=============================================
  Files          1000     1725      +725     
  Lines         25169    36148    +10979     
  Branches       2452     4760     +2308     
=============================================
- Hits          14791    10284     -4507     
- Misses         9093    24888    +15795     
+ Partials       1285      976      -309     

Impacted Files	Coverage Δ	Complexity Δ
.../log4j/v1/x/SkyWalkingContextPatternConverter.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...oolkit/log/log4j/v1/x/TraceIdPatternConverter.java	0.00% <ø> (ø)	0.00 <0.00> (?)
...m/toolkit/log/log4j/v1/x/TraceIdPatternLayout.java	0.00% <ø> (ø)	0.00 <0.00> (?)
...m/toolkit/log/log4j/v1/x/TraceIdPatternParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...m/toolkit/log/log4j/v2/x/Log4j2OutputAppender.java	0.00% <ø> (ø)	0.00 <0.00> (?)
...4j/v2/x/Log4j2SkyWalkingContextOutputAppender.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...kit/log/log4j/v2/x/SkyWalkingContextConverter.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...lkit/log/logback/v1/x/LogbackPatternConverter.java	0.00% <ø> (ø)	0.00 <0.00> (?)
...v1/x/LogbackSkyWalkingContextPatternConverter.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
.../log/logback/v1/x/TraceIdPatternLogbackLayout.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
... and 1788 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 10e89aa...fe80ab2. Read the comment docs.